6
The recommended settings on the humidistat are based on years of research
for an average building. (See
ASHRAE Handbook – HVAC Systems and
Equipment,
Ch. 20 – Humidifiers.) Note: these settings may not be appropriate
for every application. These settings represent a compromise between RH levels
that would be most desirable for comfort reasons and humidity levels that are
suitable for protection of the conditioned space and to avoid condensation on
windows and within walls. For example, a wintertime indoor RH of 50% may
be considered ideal for comfort, but unfortunately, it probably would result in
damage to the conditioned space. Observance of the recommended RH levels
on the humidistat, therefore, is an important safeguard. Condensation of
water on inside windows in the form of fogging or frost is an indication of too
much relative humidity. This same condensation can occur in other areas of
the conditioned space with the possibility of damage resulting.
TABLE 3:Outdoor–Indoor Relative Humidity
Outside Temperature
+40˚F
+30˚F
+20˚F
+10˚F
0˚F
-10˚F
-20˚F
Recommended RH
45%
40%
35%
30%
25%
20%
15%
Applies to both Automatic and Manual Operation unless indicated otherwise.
Humidifier does not
operate in “Test” mode
• Make sure equipment blower is operating and thermostat is calling for heat.
• Make sure the Outdoor Temperature Sensor is connected to the “ODT” terminals of the control.
(For Manual Operation, make sure Manual Mode Resistor Case is in place of the Sensor).
• Check main wiring diagram for correct Automatic Steam Humidifier Control installation.
• Check voltage at Automatic Steam Humidifier Control “24V” and “C” terminals.
Voltage should be 22 VDC minimum – 26 VDC maximum.
• In “Test” mode, humidifier will operate for 1 minute only. DO NOT LEAVE IN TEST MODE AS HUMIDIFIER WILL NOT OPERATE.
• Make sure water supply valve is open.
• If humidifier still does not operate, refer to the Aprilaire Steam Humidifier Installation, Operation, and Maintenance Manual.
SYMPTOM TROUBLESHOOTING PROCEDURE
Humidifier operates only
in “Test” mode
• If outdoor temperature is greater than 60°F or less than -30°F, the Automatic Steam
Humidifier Control will only operate in the “Test” mode. (Automatic Mode Only)
• If the humidity level in the building is higher than the knob setting or the proportional
control band (Model 1160 and 1180 only), the Automatic Steam Humidifier Control will not
operate the Humidifier.
• Check the resistance of the sensor by removing the leads of the Outdoor Temperature
Sensor from the terminals and measuring the resistance across the wires with an
ohmmeter. Confirm reading to outdoor temperature in Table 4.(For Manual Operation,
remove leads and verify that resistance across the leads of Manual Mode Resistor Case
is between 44,000 and 48,000 ohms).
• Make sure the Outdoor Temperature Sensor is mounted completely outside the building on the
North, East, or West side of the building and out of direct sunlight. (Automatic Mode Only)
• If Outdoor Temperature Sensor is mounted in fresh air intake duct, make sure the probe is
no more than 36 inches from the outside wall. (Automatic Mode Only)
• Make sure the Outdoor Temperature Sensor is located at least 3 feet away from all
exhaust vents. (Automatic Mode Only)
Outdoor
Temperature
-30˚F
-20˚F
-10˚F
0˚F
10˚F
20˚F
30˚F
40˚F
50˚F
60˚F
70˚F
80˚F
90˚F
100˚F
Resistance
kΩ
230.6
163.8
117.6
85.4
62.6
46.3
34.6
26.1
19.9
15.3
11.9
9.4
7.4
5.9
TROUBLESHOOTING GUIDE
TABLE 4

MANUAL MODE OPERATION NOTES

The Automatic Steam Humidifier Control is installed in the return duct.
When installed in the Manual Mode, the Control provides specific set-point
control. If the building is not designed to handle the amount of RH the
humidifier is supplying, the RH setting on the Control may need to be
adjusted to a lower value
during extreme days to
prevent condensation on
interior surfaces. For example,
with an outdoor temperature
of 20°F the correct setting will
be 35% relative humidity. If
the temperature is expected to
fall to 0°, then reduce the
setting to 25% several hours
prior to the temperature
change. It is important to
adjust the RH setting upward
when the outdoor temperature
goes back up again.
T
E
S
T
/
R
E
S
E
T
O
F
F
MANUAL MODE
%
H
U
M
I
D
I
T
Y
%
5
1
%
5
2
%
5
5
%
5
4
%
5
3
O
U
T
D
O
O
R
T
E
M
P
E
R
A
T
U
R
E
2
0
°
F
4
0
°
F
0
°
F

FIGURE 13

90-904